The invention relates to an air bag for protecting a passenger in a vehicle, such as an automobile, at an emergency time, i.e. a collision, and an air bag device including the air bag. More particularly, it relates to an air bag having a plurality of chambers therein, and an air bag device thereof.
An air bag device, as well known, is a device for expanding an air bag for receiving a passenger therewith at a collision time of an automobile or the like. The air bag is provided with a vent hole, and when the passenger hits the expanded air bag very hard, a gas in the air bag gradually flows out through the vent hole to absorb an impact.
In case an automobile speed and a physical structure of a passenger are different, a kinetic energy to a forward direction of the passenger is also varied. Thus, an air bag device satisfying the following items (1) and (2) is ideal.
(1) In case the kinetic energy to the forward direction of the passenger is large, it is preferable that a bag resistance is made large, and energy absorbing stroke and time are made long; and
(2) In case the kinetic energy to the forward direction of the passenger is relatively small, it is necessary to expand a bag to provide a small resistance against the passenger.
Japanese Utility Model Publication (KOKAI) No. 2-132555 discloses an air bag device, wherein an air bag is partitioned into two chambers separated in the vertical direction, a gas is introduced into an upper chamber through a lower chamber, and vent holes are provided to the upper side chamber. In the air bag device, at a time of collision of an automobile, first, a chest portion of the passenger is received by a first chamber having a high inner pressure, and then, a head portion of the passenger is received by a second chamber having a weak inner pressure. The air bag can not attain the above items (1) and (2).
It is an object of the invention to provide an air bag device, wherein when a passenger hits an air bag at a relatively low speed, the passenger is received by the air bag with a relatively soft touch, and in case the passenger hits the air bag at a relatively high speed, the passenger is securely received by the air bag at two stages.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In the present invention, an air bag includes a gas introducing port, a partition wall for partitioning the air bag into a first chamber having the gas introducing port and disposed on a forward side of an automobile and a second chamber disposed on a rear side thereof, a gas passage for communicating between the first chamber and the second chamber, and a vent hole disposed at the second chamber. An air bag device includes, in addition to the air bag, a gas generator for supplying gas to the air bag.
In the air bag as described above, when the gas generator is operated at a time of collision of the automobile or the like, first, the first chamber expands, and then the second chamber is expanded by the gas passing through the gas passage. In case the passenger hits the expanded air bag, the gas gradually flows out through the vent hole from the second chamber, so that an impact energy is absorbed and the passenger is received by the second chamber with a relatively soft touch. Thus, when the passenger hits the air bag with a small speed, the passenger can be sufficiently received with only a gas flow-out from the second chamber.
In case the passenger hits the air bag with a high speed, a body of the passenger also presses the first chamber from the second chamber side through the partition wall. The gas in the first chamber flows into the second chamber through the gas passage and flows out through the vent hole. Since a gas flow-out resistance at this time is large, the passenger can be securely received by the first chamber. Of course, since the gas in the first chamber is drawn into the second chamber, the impact energy of the passenger is absorbed.
As described above, since the air bag is partitioned into the first and second chambers, the passenger can be received with different impact absorbing characteristics at two stages. Incidentally, the air bag may be partitioned into first, second and third chambers or more than that.
In the present invention, it is preferable to provide a gas reverse-flow preventing device for preventing the gas from reversely flowing from the second chamber to the first chamber. With the gas reverse-flow preventing device, in case the second chamber is pressed by the passenger, a gas-reverse flow from the second chamber to the first chamber can be prevented, and a gas flow quantity for flowing out from the second chamber through the vent hole can be rationalized to thereby properly absorb the impact energy of the passenger.
The gas reverse-flow preventing device is a valve formed of a sheet. The vent hole penetrates through the sheet constituting the valve. A circumference of the vent hole provided on the sheet may be united to the air bag. Thus, when the-gas in the first chamber flows out from the vent hole through the second chamber, a flow resistance becomes large and the passenger can be sufficiently received by the first chamber.
In the present invention, it is preferable that the gas passage is disposed only on an under surface side of the air bag, or on both sides and the under surface side of the air bag. Thus, when the gas flows into the second chamber from the first chamber, the gas mainly enters a lower side of the second chamber to thereby start expanding the second chamber from the lower side. As a result, a passenger facing surface of the air bag expands to approach the passenger from the lower side thereof.
In the present invention, it is preferable that the capacity of the second chamber is larger than that of the first chamber, so that most part of the impact is absorbed by the second chamber.